In modern industrial applications, synthesizing a sinusoidal output waveform at a desired frequency and voltage has become an important issue. The power levels can be a few watts to megawatts depending on the application. This is achieved by a converter type called “inverter”. Inverters are used for uninterruptible power supply applications, or for driving motors in variable speed AC drives. Present technology for producing a power-level sinusoidal output source, generally relies on one of the two solutions, briefly described below;                a) A DC bus is created and via “pulse width modulation” techniques, a pulsed output waveform at the desired frequency is created. The modulation technique employed is such that the pulsed output waveform has a fundamental frequency component at the desired voltage level. Sometimes a filter is employed to eliminate the undesirable voltage harmonics in the synthesized waveform. The filter naturally caries the load current and can be bulky. If these voltage harmonics do not harm the function of the load, and in case the load is inductive the filter may be omitted; the inductance of the load assures that the current drawn by the load has low distortion and hence, sinusoidal shape.                    Alternatives are available based on the fundamental idea above. These may be found in many patents, papers and books available in the market.                        b) Alternatively the 3-phase mains supply is used to generate a sinusoidal output directly with the aid of devices so called “cycloconverters”. This solution however requires an expensive power stage and is only suitable for low-frequency high-power applications.        
An important requirement in many applications is reduced converter size and if possible reduced cost. Furthermore, pulsed output waveform of conventional inverters is undesirable in motor drive applications. The pulsed waveform causes stresses on the insulation. Also harmonics of the waveform cause additional power losses in the motor and this reduces the efficiency. For that reason, most motors operating with pulsed output waveforms are derated in operation. This situation occurs also for single phase motors, especially when the motor employed is of capacitor start or run type.
Another desirable feature in modern inverters is assuring that input power factor is high and high frequency harmonics are not generated towards the mains side.
The industry therefore needs a converter which is capable of;                drawing a sinusoidal current from the mains at unity power factor,        which provides isolation of the load and the mains supply,        generates a smooth sinusoidal voltage of desired magnitude at the desired frequency,        
For these reasons it is desirable to have an inverter topology overcoming the problems of the present technology, i.e.; producing a smooth output waveform with high efficiency and compact size.
The present invention here is capable of addressing all of the problems discussed in the above paragraphs and provides a solution which meets the requirements mentioned.